Oscillator circuits are used in radio frequency (RF) transceivers for radio communication. An oscillator circuit generates a signal that is used to convert frequency of an RF signal to another frequency using a mixer. In one example, the oscillator circuit generates an in-phase signal and a quadrature phase signal to down-convert the RF signal provided to an RF transceiver. The oscillator circuit down-converts the RF signal to an in-phase intermediate frequency signal and a quadrature phase intermediate frequency signal. In another example, the oscillator circuit generates the in-phase signal and the quadrature phase signal to up-convert two channels of a baseband signal for transmission. The baseband signal can be defined as a signal whose frequency is close to desired transmission or reception bandwidth. The baseband signal after up-conversion can be amplified using a power amplifier. Often, the signal after amplification has a frequency similar or in harmonic or in sub-harmonic relation to a frequency of the signal generated from the oscillator circuit and can cause frequency drift in the oscillator circuit. The frequency, of the signal after amplification, having the harmonic or the sub-harmonic relation can be referred to as harmonic frequency.
In one existing technique, the oscillator circuit includes multiple oscillators. Each oscillator can be coupled to a phase locked loop to correct the frequency drift. However, having multiple phase locked loops consumes power and increases area in an integrated circuit.
In another existing technique, the harmonic frequency is filtered out using a filter, for example a band pass filter. However, in applications of the RF transceiver where use of multiple frequency bands is desired, the harmonic frequency that is filtered out can belong to one of desired frequency band. For example, in a mobile phone that uses a global positioning system (GPS) frequency band and a global navigation satellite system (GLONASS) frequency band, a signal in the GPS frequency band can have a frequency whose harmonic is present in the GLONASS frequency band, thereby causing interference in the GLONASS frequency band. Further, signals in the GLONASS frequency band can be lost if the harmonic frequency is filtered out.